The present invention relates to a tensioner for applying constant tension to a chain or belt driving the camshaft of an automotive engine.
When a conventional tensioner is used to apply constant tension on a chain or belt, the conventional tensioner must be used together with an idling pulley or a sliding shoe. The conventional tensioner comprises a rotatable cylinder energized by a torsion spring, and a tension rod engaged by threads with the rotatable cylinder and urged in the axial direction by converting the rotating force of the rotatable cylinder into an axial, urging force of the tension rod. These components are mounted in a bored portion of the casing of the tensioner. A non-circular portion of the tension rod engages a non-circular slideway in a bearing, fixed in the casing bore, to restrain the rotation of the tension rod and to support the tension rod and rotatable cylinder. The tension rod is urged to move axially in the slideway by the threads of the rotatable cylinder to abut the belt or chain through an idling pulley or an arched, sliding shoe.
The reason the idling pulley or the sliding shoe is used between the belt or chain and the cap of the tension rod is that lateral pressure applied on the cap of the tension rod by the chain or belt in the running direction thereof functions to wear the tension rod and the belt or chain. Therefore, the idling pulley or the sliding shoe is mounted on the inner or outer wall of the engine so as to transmit an urging force of the tension rod to the belt or chain.
However, the idling pulley or sliding shoe must be mounted in a limited space such as an inner or outer wall of an engine block, and it is difficult to design adequate components; to mount and adjust them well; and to perform maintenance work on them.